Requirements for Z-scan or I-scan measurements of nonlinear optical materials I am looking to understand what requirements there are for any version of Z-Scan technique or the I-scan technique. These techniques are used for measuring nonlinear absorption and nonlinear refraction of materials and allows someone to obtain the nonlinear absorption coefficient and the nonlinear index of refraction.
The laser system that I have available to me is the Q-smart 850 by Quantel (https://www.quantel-laser.com/en/products/item/q-smart-850-mj-.html). This laser is capable of reaching 850 mJ pulse energy at 1064 nm and a Pulse Repetition Rate of 10 Hz. Further this is at a Pulse Duration ~6 ns and a Beam Diameter ~9 mm. I am trying to determine if I can do these characterization methods with this system, even if I have to modify the technique or the setup with some external component. If so, what is needed? If it is not possible, then why not?
Based on this, when I read papers in which the authors are characterizing the nonlinear properties of a material, they often list the wavelength, the pulse width, and rate it was tested at. For example, 1030 nm, 1 kHz, and 340 fs. Further, I usually see testing done in the femtosecond range.
So, can nanosecond measurements be performed (even if that means that there is no way to differentiate the nonlinear mechanisms)? What role does pulse repetition rate have on these methods? Can anyone point to where the requirements of these methods are and/or the theory that makes these the requirements? Any guidance and information here would be greatly appreciated!
 A: I'm an ultrafast specialist, so anyone with more experience with q-switched lasers might disagree, but in my opinion you cannot use nanosecond pulses for these kind of measurements. The reason why is that you need to reach a certain peak intensity to observe the effects clearly, and the problem of nanosecond pulses is that you need a lot of energy to achieve this, meaning that your fluence ($J/cm^2$) will probably be way above damage threshold....nanosecond pulses just "take too long" to get to their peak power, when most relevant damage effects occur in the picosecond range.
EDIT:
By relevant damage effects, I mean effects that will probably be present when trying to make such a measurement. In fact there are also other effects that can play a role in how energy gets deposited in the medium which have longer time-scales. But don't ask me too much about this as it's not my main specialization.
And secondly, even if below damage threshold, thermal lensing could obscure any nonlinear effect.
